Journal of Applied Physiology, Vol 62, Issue 6 2314-2319, Copyright © 1987 by American Physiological Society
Contractile properties of expiratory abdominal muscles: effect of elastase-induced emphysema
J. S. Arnold, A. J. Thomas and S. G. Kelsen
The present study examined the intrinsic contractile properties and
endurance of the transverse abdominis and external oblique abdominal
expiratory muscles in adult hamsters and compared their performance with
the diaphragm. Experiments were performed in vitro on isolated bundles of
muscle stimulated electrically. In control animals peak twitch tension was
similar in the two muscles. In contrast, the twitch contraction time and
one-half relaxation time of the transverse abdominis were significantly
greater than that of the external oblique. The isometric tension generated
over a range of stimulus frequencies (i.e., the force-frequency
relationship) was a greater percent of the maximum value in response to
subtetanizing frequencies (10-40 Hz) in the transverse abdominis than in
the external oblique. For both abdominal muscles, however, the tension
generated over this range of stimulus frequencies was less than that of the
diaphragm. The endurance of the transverse abdominis during repeated
contractions was significantly greater than that of the external oblique
but similar to the diaphragm. The effect of chronic hyperinflation produced
by elastase-induced emphysema on the contractile function of the two
muscles was assessed in a second group of adult hamsters. In emphysematous
animals peak twitch tension, contraction time, and one-half relaxation time
of the twitch and force-frequency curves of muscles from emphysematous
animals were similar to values obtained in control animals for both the
external oblique and transverse abdominis. However, the endurance of both
the transverse abdominis and external oblique muscles was greater in
emphysematous than control animals.(ABSTRACT TRUNCATED AT 250 WORDS)
